The invention relates to a clutch operating cylinder for a pressure-medium operated clutch, with a release piston which is axially displaceable in a cylindrical housing and acts via a push rod on a clutch release fork imposed by a restoring spring. Such an arrangement is generally known in hydraulic clutch operation.
For vehicles having anti-slip regulation, under certain conditions the drive power of the engine is temporarily reduced. In order to eliminate the associated engine drag moment while making comfortable starting possible, for example on an upward incline, an electrically controlled intervention in the clutch operation is expedient.
As with all interventions in the driving and braking of a vehicle, for example anti-slip regulation and an anti-blocking system, a high degree of safety is necessary. Consequently, it is desirable that the electronic control not clutch further than is specified by the driver via the clutch pedal. If the control is used to declutch, it is advantageous if the counter pressure at the clutch pedal does not change. It is desirable for partial operation of the clutch performed by the control (half-declutched) to be overridden at any time by the driver, in other words, the driver is able to fully declutch by pedal operation.
It is an object of the invention to provide a pressure-medium operated clutch in which a controlled clutch operation is superimposed on the pedal-operated clutch, while the above-mentioned safety conditions are met.
This and other objects are achieved by providing a clutch operating cylinder with a release piston which is axially displaceable in a cylindrical housing and which acts via a pushrod on a clutch release fork imposed upon by a restoring spring. The cylinder includes a partition which divides the housing into first and second chambers, the release piston having a rest position in an axially middle region of the first chamber. A second coaxial piston in the first chamber has a rest position substantially adjacent the partition. The cylinder includes a third coaxial piston in the second chamber and spring means between the partition and the third coaxial piston for holding the third coaxial piston in a rest position at a first end wall of the housing. First and second piston rods on either side of the second coaxial piston are provided, with the first piston rod supporting the release piston when the release piston is in the rest position, while the second piston rod extends through the partition and contacts the third piston in the rest positions of the second and third coaxial pistons. The cylinder also includes a pressure medium line connectable to an input cylinder of the clutch and opening both through the first end wall into the second chamber and into the first chamber close to the rest position of the release piston between the release piston and the second coaxial piston. A further pressure medium line is connectable to a pressure accumulator and can be shut off, this further pressure medium line opening into the first chamber between the partition and the second coaxial piston.
As shown below, all safety requirements demanded are met by this apparatus. The special advantages are the simple design and, consequently, the inexpensive production, long service life and reliable functioning of the clutch operating cylinder.
Further details of the invention are to be taken from the subsequent description of an exemplary embodiment. It relates to a clutch operating cylinder since this is the easiest way of superimposing the desired function on the pedal-operated function. However, it is also contemplated to provide a correspondingly designed clutch input cylinder, or for it to act in parallel with the clutch operating cylinder on the release fork.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.